Compressor employing radial diffusion



M r h 19, 1957 E. A. STALKER 2,785,849

COMPRESSOR EMPLOYING RADIAL DIFFUSION Filed June 1948 2 Sheets-Sheet 1 2 I; \5 f 1' '23 31 5 I l 11; I 1 l I L 5 J 5 Flll 12 I N VE TOR.

March 19, 1957 E. A. STALKER 2,785,849

COMPRESSOR EMPLOYING RADIAL DIFFUSION Filed June 21, 1948 2 Shee ts-Sheet 2 a I f 36 i %36 1N VEN TOR.

United States Patent This invention relates to compressors of the type known as the axial-flow compressor. In this invention the passages between blades increase in radial depth resulting in radial diffusion of the flow, a principle that will be further applied and discussed in the following description and explanation of the accompanying drawings.

It is an object of this invention to provide an eificient high-pressure compressor of low fabrication cost.

In particular it is the object of this invention to provide an etficient and relatively high compression per stage, by other means than that of peripheral diffusion in curved passages formed by expensive curved vanes or blades.

It is another object to utilize a multiplicity of these stages in coaxial combination. They may have successively shorter axial dimension as the pressure increases so as to reduce the length of such a combination to a minimum.

Still another object is to provide a compressor having a high pressure coefiicient for a large range of delivery expressed as the volume per revolution or as Cml/U where Cmi is the absolute axial velocity and U' is the peripheral velocity of the rotor. A

Other objects will appear from the following description, the accompanying drawings, and the appended claims.

I accomplish the above objects by the means illustrated in the accompanying drawings in which- Figure l is a vertical quarter section of an 8-stage compressor, showing the axial disposition of the various stages;

Figure 2 is an enlarged fragmentary developed view of the compressor rotor and stator vanes looking inboard normal to a plane represented by line 22 of Figure 1;

Figure 3 is an enlarged radial section of a typical rotor straight diffuser passage taken along center line 33 of Figure 2;

Figure 4 shows a typical vector diagram for a single 7 compressor stage operating at design conditions;

Figure 5 shows a method of fairing the entrance noses of the various vanes so as to increase the off design performance of the unit;

Figure 6 is the rear view of a blade in elevation;

Figure 7 is a section of the blade along the line 7-7 in Figure 6;

, Figure 8 is a section of the blade along the line 8-8 in Figure 6;

igure 9 is the .vector diagram for the root and tip sections of'the blade in Figure 6;

Figure 10 is 'an axial part section through a multi-stage radial diffusion rotor with curved blades like those of Figure 6 and with special stators;

'Figure 11 is a'fragmentary development of a radial diffusion stage showing another form of stator blade;

Figure 12 is a view from the line 1212 in Fig. 11; Figure 13 is a vector diagram for the flow past the tip portions of the stator blades of Figure 11 shown in relation to a rotor stage;

2,785,849 Patented Mar. 19, 1957 Figure 14 shows still another form of rotor blade having twisted leading edge portion; and

Figure 15 shows the curves of pressure coeflicient versus the flow parameter for a peripheral difiusion compressor and a radial diffusion compressor;

Other applications which have been filed show the means of pumping by rotor passages diffusing by means of radial expansion. These are Serial No. 593,631, filed May 14, ,1945, now Patent No. 2,648,492, Serial No. 624,013, filed October 23, 1945, now Patent No. 2,648,493, Serial No. 687,385, filed July 31, 1946, now Patent No. 2,732,999, and Serial No. 794,018, filed December 26,

1947, now Patent No. 2,749,027. The present application difiers from the preceding in disclosing a multi-stage arrangement of radial diffusion rotor stages and stators, and in special shapes of rotor and stator blades as well as differently shaped stator passages.

All present day multiple-stage high performance axialfiow compressors use curved blades or vanes forming curved expanding passages between them. The passages expand peripherally. The diffusing therefore takes place peripherally in a peripherally curved passage against a rising pressure. This leads to poor local efiiciencies and definitely limits performance in regard to the permissible pressure ratio per stage. When efiiciency is required, the fabrication costs of a compressor utilizing curved blades of the type required by peripheral difiusion weigh against their consideration for use in many commercial applications.

' The compressor as shown consists of outer stator support case 1 from which the rotor drum assembly 3 is supported by means of bearing assemblies 5 and 7 and support vanes 9 and 11. The rotor assembly 3 is driven in the direction indicated on Figure 1 by means of splined shaft 13 supported by bearing assembly 7 and attached to end plate '15 of rotor assembly 3 by means of bolts 17.

All compressor stages are similar, so, for simplicity of explanation, only the first stage of the compressor need be described. In the following discussion air will be assumed as the medium for compression, although this compressor could be designed to pump any compressible fluid-or a non-compressible fluid, if desired, in which case all stages would be identical.

Inducted air enters the compressor past the streamlined support vanes 9, arriving at plane A Figure 1 with an axial velocity of ab=C1 as shown in the vector diagram of Figure 4. The blade peripheral velocity Un, represented by velocity vector be, when added vectorially to axial velocity C1, gives an oblique relative entering velocity of ac=V1 at angle a with respect to plane A at the entrance to the rotor stage as shown in Figure 4.

Referring to Figures 1 and 2, the oblique rotor diffuser passages 19 between planes A and B are formed by the surfaces of the oblique straight vanes or blades 21 at angle on to plane A, the rotor-drum outer-truncated cone surface 23, and the outer-truncated cone-shaped ring 25, both of the latter being rounded at the entrance following plane A so as to give a smooth approach to the expanding portion of the diffuser passage 19. Figure 3 shows an enlarged radial section of a typical rotor stage straight diffuser passage taken along center line 33 of passage 19, Figure 2. It will be noted that the rotor blades 21 in the developed view of Figure 2 are parallel.

Thus, by the time the air reaches plane B leaving the rotor stage its relative velocity with respect to the exit of rotor vanes 21 has been reduced to a value represented by relative velocity vector cd=Vz of Figure 4. Subtrac- V 7 equal to the initial entrance velocity ready to repe'at the 'samesvectorpattern'in the next stage traction; occurring between planes 'alent area of flow as the air passes 'net change in"peripheral velocity of the peripheral velocity of the' rotor at the layer is persuaded to .of the vanes.

locity (ACu) to the air ajtl 7 V root. Sections at the root'and tip are shown'in Pigs. 7 7

160 The vector diagram for the blade of Fig. ,6 is shown a V "tip sections.

' B. It is the purpose of the stator passages 29, formed by the surfaces; of the vanes 27 the internal shroud 31 and v the case 1, to initially difiuse the air to a low velocity in a straight line from planes B to C and then to make ariaccelerating turn from plane C to the exit plane D such that the air leaves the stator in an axial direction at plane D with a velocity-vector cf, Figure 4, essentially vector ab so as lobe of compression. This necessitates a sinusoidal type corn 7 C and D in Figure 1, designed such that there is a continually decreasing equivplane D. c a c The'static pressure rise for a stage is i V 7 P= UACu '(1) where p isrthe mass density ofthe 'liuid and ACu' is the fluid. U is the diameter where AC is measured. Ordinarily it is the In Fig. 4 the absolute velocity is C1 which in this case is identical with the absolute'axial velocity Cmi. A01 is the peripheral component of the absolute vector C2 equal to ce. 7 7

Figures 1 and 3 show the passage 1? with walls diverging equally with respect to the line 22. They also show the inner wall 23 as straight axially but curved as a result, along line 3-3. Where it is desired to make the angle of divergence of the walls quite large so as to shorten the machine still more all the divergence may be given to the outer wall (of passage 19) and the inner Wal mayi be made straight in the direction 3 3 of Figure 2.. The centrifugal pressure of the air will suppress the t endency for the flow to separate from the outer wall, making it possible for this Wall to diverge quickly from line 2-2. In this formof this invention the flow in the stator is' expanded and reduced in velocity where the vanes are substantially -straight and accelerated where 'they are curved; By accelerating the flow. at the turn, the boundary stick to and follow the convex side This'eliminates' separation of the flow with its attendant 'loss of head. I

The compressor of Fig. 1 may be given other blade forms than those shown in Figs. 2 and 5. The. forms of these figures are suitable for small hub ratios, that is the ratio of the hubdiameter to the tip diameter 'of the rotor stage. For best efficiency the huoratio'is not smaller than about 0.85 when the blades'are simple fiat sheets. 7 I V e The hub ratio maybe made smaller, of the order of 0.7, by curving at least a portion of each'blade. V V 6 to 8 the-trailing edge (T. E.) of the rotor blade'36 is twisted'rso that In one example shown in Figs.

theblade does not contribute quite as much whirl-lye- .the .bladetip as at. the blade and I 8 respectively.

in Fig; 9. The axial velocity Cmi is the same for root'and The whirl ve'locity sou added to the-air bythe hat.

of the rotor stage is ACm: and Acur for the root aud ltip sections respectively because-of the twist; If the blade were not twisted the product UllCu would be different for the root and tip=portions ofthe blade and losses from plane .(3 to mean diameter;

The peripheral velocities are Ur andUej' .The relative velocities are V11 andl/Tn. V

the tips and increases it at the root.

4 tip and root portions of the blade. This is so since C21 and C21; are different in magnitude.

To convert the dynamic head added by each rotor stage, stators of special design are required.

The stator passages 42 shown in Fig. 10 do not have a radially expanding inlet portion but each has a radially decreasing widthor depth from inlet to exit,

The stators shownin Fig. 10 are designed to bring the flow received from the rotor to a constant axial velocity along the radial extent of the blade at the trailing 1 edge.

tends to bring the flow to equality with the velocity and static .pressure of the'streamlines 48 originally having a the velocity C2r;

The rotor stagesand blades of developed view are similar to the blades 27 of Fig. 2. As shown in Figs. ll, 12 and 13 the stator structure may have blades as twisted along the trailing edge to serve the purpose of permitting the rotor stage to add equal amounts UACu at the root and tip portions. It is to be recalled that A04 is the increment of whirl velocity added by the rotor stage. Heretofore the absolute velocity ahead of the rotor stage has been taken as axial. This need not be the case and in Figs. ll and 12 the tip portions of the stator blades direct the flow in the direction of rotor blade rota-tion and'against the direction of rotation at the root. This reduces'the eifective whirl velocityat In Fig. 13 the fluid has the initial peripheral component Cul while the rotor adds the amount Cuz. 7 Then bring the head into equality with that of the fluid flowing past the root portions. Various combinations of stator and rotor blade twist may be employed andas shown on blade 70 in Fig. 14

theleading edge portions may be twisted.

In order to keep the overall diameter within certain limits it maybe desirable :to' use a smaller difiusion ;through the rotor in the earlier stages as compared to the later or downstream stages. Thus the ratio of exit area AztO inletarea A1 of the passage through a' rotor may be of the order of 1.25 for the first stage and 3 for the last stage with a progressive increase in the valuebe- V tween the outer stages;

' rotor passages;

. compressor.

The radial diffusion rotor stage is characterized by the expansion of the fluid radially as its flows through the The inlet of each passage of a stage is at substantially the same radius as the exit thereof. The a r axial length of a rotor stageis ordinarily of the order of the maximum radial depth of the flow passage'of a jrotor stage. Furthermore the axial length of the rotor stage is small compared to the diameter of the rotor 'stage, preferably aminor portion of the'diarneter.

Figure 15 shows. the curves of pressure coeflicient Cp versus flow parametenfor a vperipheral .difEusionof'con ventional, axial flow compressor and. fora radial diffusion f 5 They are respectively cunvesj 80 and 82. I

' This coeflicient is found by dividing the pressure rise of isthesamc at root and tip although the division of total the stage by U /2;

fThe radialidiffusion rotor the conventional axialflow machine. 'The rotorpassages liein the rotor and rotate with it.

Fig. were similar to those of Figs. 1 and 2. The stators blades as'seen in the i stage presents .a high pifes sure for a much Wider range 'of Cmiyu. ln factfit can operate overca range of Can u several times Ia's great as" V myself to this exact form but intend to claim my invention broadly as indicated by the appended claims.

I claim:

1. In combination in an axial-flow compressor, a casing adapted'to have a flow of fluid therethrough, rotor stage mounted in said casing for rotation about its axis to induce a flow through said compressor, means to rotate said rotor stage, said rotor stage having a plurality of passages therethroug'h, each directed to an exit facing rearward to discharge fluid rearward in the general axial direction, each said passage having an inner wall and an outer Wall spaced radially outward therefrom, said walls diverging in a downstream direction along the length of said rotor, and a stator positioned in said casing downstream from said rotor stage, said stator having a plurality of blades forming a plurality of through passages therebetween, said stator passages being adapted to receive said flow therethrough from said rotor stage, said stator blades having substantially straight upstream portions extending along the chordwise direction followed by a portion of substantial chordwise curvature, said passage between blades increasing in cross sectional area in the downstream direction along said upstream portions and decreasing in cross sectional area along said curved portions in the downstream direction.

2. In combination, in a compressor, a casing, a hub within said casing defining therewith an annular space therebetween, means supporting said hub for rotation about its axis, a rotor stage including a plurality of rotor blades supported on said hub to divide said annular space into a plurality of passages distributed peripherally about said hub, each said passage lying substantially along said axis and having an exit facing rearward to discharge fluid rearward in the general direction of said axis, each said passage having increasing width and cross sectional area along the rearward direction, and a plurality of stator blades supported aft of said rotor blades in said casing peripherally thereabout forming a plurality of fluid flow stator passages, each said stator passage increasing radially in cross sectional area rearwardly along the forward portions of said stator passage and decreasing in cross sectional area rearwardly along the rearward portions thereof.

3. In a compressor of the axial-flow type, a rotor stage to impel the flow of fluid along its axis of rotation, said rotor stage having a rotor flow passage expanding downstream along said axis With increasing cross sectional area, each said passage lying substantially along said axis and having an exit facing rearward to discharge fluid rearward in the general direction of said axis, and a stator adapted to direct a flow of fluid from said rotor stage, said stator having a stator flow passage whose forward portion is tapered to increase gradually in cross sectional area downstream with increasing radial Width succeeded by a portion of gradually decreasing cross sectional area.

4. In a compressor of the axial-flow type, an axial flow rotor stage to impel the flow of fluid along its axis of rotation, said rotor stage having a rotor flow passage expanding downstream along said axis with increasing radial width, each said passage lying substantially along said axis and directed to an exit facing rearward to discharge fluid rearward in the general direction of said axis, and a stator adapted to direct a flow of fluid from said rotor stage, said stator having a stator flow passage whose forward portion increases in cross sectional area in the downstream direction with increasing radial Width succeeded by a portion of decreasing cross sectional area, said rotor passage being substantially straight in the rearward direction therethrough.

5. In an axial flow compressor, in combination, a hub mounted for rotation about an axis, and a plurality of blades disposed on said hub peripherally thereabout defining a plurality of rotor stage passages, each said blade making a substantial pitch angle with said axis with the nose of said blade being deflected forwardly in the direction of rotation, each said passage having a greater radial depth and area at exit than at inlet, each said passage having an exit facing rearward to discharge fluid rearward in the general direction of said axis, each said blade having its aft portion at its outer radial end curved backward with respect to the peripheral direction in which the nose of said blade points.

6. In an axial flow compressor, in combination, a hub mounted for rotation about an axis, and a plurality of blades disposed on said hub peripherally thereabout defining a plurality of rotor stage passages, each said blade making a substantial pitch angle with said axis with the nose of said blade beingdeflected forwardly in the direction of rotation, each said passage having a greater radial depth and area at exit than at inlet, each said passage directed to an exit facing rearward to discharge fluid rearward in the general direction of said axis, each said blade having its aft portion at its outer radial end twisted backward with respect to the peripheral direction in which the nose of said blade points, each said blade having its aft portion at its inner radial end curved forward with respect to said direction. I

7. In an axial flow compressor, in combination, an axial flow rotor stage mounted for rotation about an axis, said rotor stage having a plurality of axial flow passages therethrough, each said passage having a greater radial depth and area at exit than at inlet, each said passage being directed to an exit facing rearward to discharge fluid rearward in the general direction of said axis, a plurality of stator blades positioned ahead of said rotor stage to direct a flow of fluid into said flow passages of said rotor stage, each said stator blade having its aft portion at its outer radial end curved forward with respect to the direction of rotation of said rotor stage to give some fluid a component of velocity in the direction of rotation of said rotor stage. t

8 In combination in an axial flow compressor, a case adapted to have a flow of fluid th'erethrough, and an axial flow rotor stage mounted in said case for rotation about its axis to induce a flow through said compressor, said rotor stage having a plurality of blades disposed in spaced relation peripherally thereabout, the radii of the tips of the blades increasing in the downstream direction, said rotor stage having an axial length of the order of the maximum radial length of said blades, said blades defining passages therebetween each increasing in cross sectional area and radial width along said axis in the downstream direction with the cross sectional area of each passage exit being larger than the cross sectional area of each passage inlet, each said passage having its said exit facing rearward to discharge fluid rearward in the general direction of said axis.

9. In combination in a compressor, a plurality of rotor stages each having a plurality of blades supported thereon to impel a fluid flow, said rotor stages being mounted in tandem for rotation about their axes, said blades defining flow passages therebetween, each said rotor passage having an exit facing rearward to discharge fluid rearward in the general direction of said axis, each said passage expanding radially downstream to said exit greater than the inlet in cross sectional area and radial depth, a casing to house said rotor stages and flow of fluid, and a stator structure interposed between a pair of said rotor stages, said stator comprising a plurality of stator blades peripherally spaced apart in the same transverse plane to define therebetween a plurality of peripherally adjacent stator passages, each said stator blade being tapered in radial depth with the leading edge longer than the trailing edge to provide inlet areas greater than the exit areas of said stator passages.

10. In combination in a compressor, a case, and an axial flow rotor stage including a plurality of blades mounted in said case for rotation about an axis to impel fluid through said case in the general axial direction, the radii of the tips of the blades increasing in the downstream direction, said rotor stage having a passage with inlet and exit rotatable with said rotor stage, said exit having a greater radial depth and a greater cross-sectional area than said inlet to provide a pumping action, the ratio of said exit to said inlet cross sectional areas being in the range of about 1.25 tofabout 3.0,s'aid exit having its radially inward side substantially nearer said axis than the cor responding side of said inlet, said passage being set peripherally obliquely to said axis to receive a fluid flow thereinto directed parallel'to the inlet portion of said passage while providing said pumping action on said fluid.

11. In combination in an axial flow com ressor, a

plurality of rotorsta-ges disposed in tandem for rotation about an axis, each said rotor stage having a plurality of axial flow passages therethrough, each said passage having an exit facing rearward to discharge fluid rearward in the general direction of said axis, each said passage having a greater radial depth and cross sectional area at the exit thanat the inlet thereof, the radial depth of the inlet of a downstream rotor stage being less than the radial ,depth'of the exit of the adjacent upstream rotor stage, and av stator means positioned between said adjacent, upstream and downstream rotor stages, said stator means havingpassages therethrough to direct fluid from said upstream rotor stage to said downstream rotor stage, each said stator passage conforming in depth at its ends to the radial depth of the respective rotor passage portion adjacent thereto. 12. In combination in an axial flow compressor, a case adapted to have a flow of fluid therethrough, and a rotor stage mounted in said case for rotation about its axis to induce a flow through said compressor, said rotor stage having a plurality. of' blades disposed in spaced relation peripherally thereabout, the radii of the tips of the blades increasing in the downstream direction, said blades defin in-g passages therebetween increasing in cross sectional area and radial depth along said axis in the downstream direction with the exit cross sectional areas greater than the inlet cross sectional areas of said rotor assages each said passage being directed to an exit facing rearward to discharge fluid rearward in the general direction of said axis, each'said' passage having-a ratio of said exit area to said inlet area within the range of about 1.25 to 3, the axial length of said rotor stage being less than a minor fraction of the maximum'diameter. thereof.

13. In combinationin an axial flow machine for increasing the pressure of an elasticfluid, a case adapted to have a flow of elastic fluid the'rethrough, and a rotor stage mounted in said ease for rotation about an axis to induce al'iow through said machine, said rotor stage 7 having a plurality of blades disposedin spaced relation peripherally thereabout at a substantial pitch angle with respect to said axis, each said blade having a greater forward chordwise curvamre at the radially inward aftportion thereof than at the outer aft portion thereof, said blades defining passages therebetween increasing in cross sectional area and radial depth in the downstream'direction with the exit cross sectional areasgreater than the inlet cross sectional areas, each said passage being directed to an exit facing rearward to discharge fluid rearward in the general direction of said axis,each said passage 'having a ratio of said exit area to said inlet area within the. range I of about 1.25 to 3.0.

References Cited in the file of this patent UNITED STATES PATENTS France Mar. 6, 1925 

